residents being told to expect a continued heightened law enforcement presence as the city tries to come to grips with a violent attack in the heart of boston. and that was katie davis there with that report. now london's metropolitan police are reviewing security plans for this sunday's marathon after the explosion in boston. the minister told bbc the best way to show solidarity with boston is to continue the race as the french president has stepped up security around public buildings in this country and raised the threat level to red. >>> speaking earlier, it was said the long lasting impact of terrorist attacks are low. >> research into terrorist incidents over many, many years, their economic impact, their direct economic impact tends to be very, very small, indeed. a lot of good research done on this in israel. what i would say is yes, of course, very often the economic cost is largely in how we react. what new measures are put in place to counter this sort of thing often i'm afraid a certain amount of closing the stable door after the horse has bolted. i'm afraid we live in a world